Ketone bodies could support the motility but not the acrosome reaction of mouse sperm

Effect of Metformin on Sertoli Cell Fatty Acid Metabolism and Blood-Testis Barrier Formation

Sertoli cells (SCs) are essential to maintaining germ cell development. Metformin, the main pharmacologic treatment for pediatric type 2 diabetes, is administered to children during SC maturation. The present study aimed to analyze whether metformin affects SC energy metabolism and blood-testis barrier (BTB) integrity. Primary SC cultures were used for the in vitro studies. In vivo effects were studied in Sprague-Dawley rats treated with 200 mg/kg metformin from Pnd14 to Pnd30. Metformin decreased fatty acid oxidation and increased 3-hydroxybutyrate production in vitro. Moreover, it decreased the transepithelial electrical resistance across the monolayer and induced ZO-1 redistribution, suggesting an alteration of cell junctions. In vivo, a mild but significant increase in BTB permeability and ZO-1 expression was observed in the metformin group, without changes in testicular histology and meiosis progression. Additionally, adult rats that received metformin treatment during the juvenile period showed no alteration in BTB permeability or daily sperm production. In conclusion, metformin exposure may affect BTB permeability in juvenile rats, but this seems not to influence spermatogenesis progression. Considering the results obtained in adult animals, it is possible to speculate that metformin treatment during the juvenile period does not affect testicular function in adulthood.

A Metabolomic Analysis to Assess the Responses of the Male Gonads of Mytilus galloprovincialis after Heavy Metal Exposure

In recent years, metabolomics has become a valuable new resource in environmental monitoring programs based on the use of bio-indicators such as Mytilus galloprovincialis. The reproductive system is extremely susceptible to the effects of environmental pollutants, and in a previous paper, we showed metabolomic alterations in mussel spermatozoa exposed to metal chlorides of copper, nickel, and cadmium, and the mixture with these metals. In order to obtain a better overview, in the present work, we evaluated the metabolic changes in the male gonad under the same experimental conditions used in the previous work, using a metabolomic approach based on GC-MS analysis. A total of 248 endogenous metabolites were identified in the male gonads of mussels. Statistical analyses of the data, including partial least squares discriminant analysis, enabled the identification of key metabolites through the use of variable importance in projection scores. Furthermore, a metabolite enrichment analysis revealed complex and significant interactions within different metabolic pathways and between different metabolites. Particularly significant were the results on pyruvate metabolism, glycolysis, and gluconeogenesis, and glyoxylate and dicarboxylate metabolism, which highlighted the complex and interconnected nature of these biochemical processes in mussel gonads. Overall, these results add new information to the understanding of how certain pollutants may affect specific physiological functions of mussel gonads.

IKBA phosphorylation governs human sperm motility through ACC-mediated fatty acid beta-oxidation

The nuclear factor-κB (NF-κB) signaling pathway regulates specific immunological responses and controls a wide range of physiological processes. NF-κB inhibitor alpha (IKBA) is an NF-κB inhibitory mediator in the cytoplasm that modulates the nuclear translocation and DNA binding activities of NF-κB proteins. However, whether the upstream cascade of the canonical NF-κB signaling pathway has physiological roles independent of IKBA-mediated transcriptional activation remains unclear. Herein we investigated the function of IKBA in mature sperm in which transcriptional and translational events do not occur. IKBA was highly expressed in human sperm. The repression of IKBA phosphorylation by its inhibitor Bay117082 markedly enhanced sperm motility. On the contrary, lipopolysaccharide-stimulated IKBA phosphorylation significantly decreased sperm motility. Nevertheless, Bay117082 treatment did not affect the motility of IKBA-knockout sperm. Further, untargeted metabolomic analysis and pharmacological blocking assays revealed that the Bay117082-induced increase in sperm motility was attributable to fatty acid β-oxidation (FAO) enhancement. In addition, we found that IKBA phosphorylation inhibition resulted in a significant reduction of acetyl-CoA carboxylase levels in the FAO metabolic pathway. Our findings indicate that IKBA-mediated signaling orchestrates sperm motility program and improves our understanding of transcription-independent NF-κB signaling pathway in cells.

Motility Assessment of Ram Spermatozoa

For successful fertilisation to occur, spermatozoa need to successfully migrate through the female reproductive tract and penetrate the oocyte. Predictably, poor sperm motility has been associated with low rates of fertilisation in many mammalian species, including the ram. As such, motility is one of the most important parameters used for in vitro evaluation of ram sperm quality and function. This review aims to outline the mechanical and energetic processes which underpin sperm motility, describe changes in motility which occur as a result of differences in sperm structure and the surrounding microenvironment, and assess the effectiveness of the various methods used to assess sperm motility in rams. Methods of subjective motility estimation are convenient, inexpensive methods widely used in the livestock industries, however, the subjective nature of these methods can make them unreliable. Computer-assisted sperm analysis (CASA) technology accurately and objectively measures sperm motility via two-dimensional tracing of sperm head motion, making it a popular method for sperm quality assurance in domesticated animal production laboratories. Newly developed methods of motility assessment including flagellar tracing, three-dimensional sperm tracing, in vivo motility assessment, and molecular assays which quantify motility-associated biomarkers, enable analysis of a new range of sperm motion parameters with the potential to reveal new mechanistic insights and improve ram semen assessment. Experimental application of these technologies is required to fully understand their potential to improve semen quality assessment and prediction of reproductive success in ovine artificial breeding programs.

Curcumin Remedies Testicular Function and Spermatogenesis in Male Mice with Low-Carbohydrate-Diet-Induced Metabolic Dysfunction

Increasing reports on the significance of dietary patterns in reproduction have arisen from both animal and human studies, suggesting an interactive association between nutrition and male fertility. The aim of this study was to investigate the effects of curcumin supplementation on low-carbohydrate-diet-induced metabolic dysfunction, testicular antioxidant capacity, apoptosis, inflammation and spermatogenesis in male mice. Male C57BL/6 mice were fed a normal diet (AIN-93M group, n = 12) and a low-carbohydrate diet for 12 weeks (LC group, fed with low-carbohydrate diet, n = 48), and mice randomly chosen from the LC group were later fed their original diet (LC group, n = 12). This diet was changed to AIN-93M feed (LC/AIN-93M group, n = 12), a ketogenic diet (LC/KD group, n = 12), or a ketogenic diet treated with curcumin supplementation for the final 6 weeks (LC/KDCu group, n = 12). A poor sperm morphology and mean testicular biopsy score (MTBS) were observed in the LC and LC/KD groups, but they were eliminated by the normal diet or ketogenic diet with curcumin. The LC group exhibited a lower testicular testosterone level and a lower 17β-HSD activity and protein expression. This also enhanced apoptosis protein expressions in testis tissue, including Bax/BCl₂, cleaved caspase 3, PARP and NF-κB. Meanwhile, we found a statistically significant increase in lipid peroxidation and decreased superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase levels in the LC group. Our study indicated that a replacement of a normal diet or ketogenic diet supplemented with curcumin attenuated poor semen quality and reduced testosterone levels by the LC diet by reducing oxidative stress.

Is a Ketogenic Diet Superior to a High-Fat, High-Cholesterol Diet Regarding Testicular Function and Spermatogenesis?

The study aimed to determine effects of a ketogenic diet on metabolic dysfunction, testicular antioxidant capacity, apoptosis, inflammation, and spermatogenesis in a high-fat and high-cholesterol diet-induced obese mice model. Forty-two male C57BL/6 mice were fed either a normal diet (NC group) or a high-fat and high-cholesterol (HFC) diet (HFC group) for 16 weeks, and mice from the HFC group were later randomly divided into two groups: the first were maintained on the original HFC diet, and the second were fed a medium-chain triacylglycerol (MCT)-based ketogenic diet for 8 weeks (KD group). A poor semen quality was observed in the HFC group, but this was eliminated by the ketogenic diet. Both the HFC and KD groups exhibited enhanced apoptosis protein expressions in testis tissue, including caspase 3 and cleaved PARP, and higher inflammation protein expressions, including TNF-α and NF-κB. However, the KD group exhibited a statistically-significant reduction in lipid peroxidation and an increased glutathione peroxidase level as compared with the HFC group. The HFC diet induced obesity in mice, which developed body weight gain, abnormal relative organ weights, metabolic dysfunction, and liver injury. Overall, the results showed that a ketogenic diet attenuated oxidative stress and improved the semen quality reduced by the HFC diet.

K. M, Karthikkeyan G, Prasad TSK, Modi PK, Datta TK, Ramesha K, Manimaran A, Jeyakumar S. Deep Metabolomic Profiling Reveals Alterations in Fatty Acid Synthesis and Ketone Body Degradations in Spermatozoa and Seminal Plasma of Astheno-Oligozoospermic Bulls

Male fertility is extremely important in dairy animals because semen from a single bull is used to inseminate several thousand females. Asthenozoospermia (reduced sperm motility) and oligozoospermia (reduced sperm concentration) are the two important reasons cited for idiopathic infertility in crossbred bulls; however, the etiology remains elusive. In this study, using a non-targeted liquid chromatography with tandem mass spectrometry-based approach, we carried out a deep metabolomic analysis of spermatozoa and seminal plasma derived from normozoospermic and astheno-oligozoospermic bulls. Using bioinformatics tools, alterations in metabolites and metabolic pathways between normozoospermia and astheno-oligozoospermia were elucidated. A total of 299 and 167 metabolites in spermatozoa and 183 and 147 metabolites in seminal plasma were detected in astheno-oligozoospermic and normozoospermic bulls, respectively. Among the mapped metabolites, 75 sperm metabolites were common to both the groups, whereas 166 and 50 sperm metabolites were unique to astheno-oligozoospermic and normozoospermic bulls, respectively. Similarly, 86 metabolites were common to both the groups, whereas 45 and 37 seminal plasma metabolites were unique to astheno-oligozoospermic and normozoospermic bulls, respectively. Among the differentially expressed metabolites, 62 sperm metabolites and 56 seminal plasma metabolites were significantly dysregulated in astheno-oligozoospermic bulls. In spermatozoa, selenocysteine, deoxyuridine triphosphate, and nitroprusside showed significant enrichment in astheno-oligozoospermic bulls. In seminal plasma, malonic acid, 5-diphosphoinositol pentakisphosphate, D-cysteine, and nicotinamide adenine dinucleotide phosphate were significantly upregulated, whereas tetradecanoyl-CoA was significantly downregulated in the astheno-oligozoospermia. Spermatozoa from astheno-oligozoospermic bulls showed alterations in the metabolism of fatty acid and fatty acid elongation in mitochondria pathways, whereas seminal plasma from astheno-oligozoospermic bulls showed alterations in synthesis and degradation of ketone bodies, pyruvate metabolism, and inositol phosphate metabolism pathways. The present study revealed vital information related to semen metabolomic differences between astheno-oligozoospermic and normospermic crossbred breeding bulls. It is inferred that fatty acid synthesis and ketone body degradations are altered in the spermatozoa and seminal plasma of astheno-oligozoospermic crossbred bulls. These results open up new avenues for further research, and current findings can be applied for the modulation of identified pathways to restore sperm motility and concentration in astheno-oligozoospermic bulls.

High concentrations of β-hydroxybutyrate alter the kinetics of bovine spermatozoa

Postpartum cows, mainly with metabolic diseases, such as ketosis, usually experience an increased number of services per conception. During ketosis, high concentrations of β-hydroxybutyrate (BHBA) in follicular, uterine and oviductal fluid have been considered to cause subfertility in cows. However, the effect of sperm exposure to an environment with high BHBA concentration is not known. This study investigated the influence of high levels of BHBA on kinetics, oxidative status and morphology of bovine spermatozoa. To assess the effect of BHBA after sperm selection, bovine spermatozoa were incubated (180 min) with different BHBA concentrations: 0 (Control), 0.8, 2.4 or 5 mM. Sperm kinetics was evaluated after 30, 60, 120 and 180 min, and oxidative status and morphology were analysed at 180 min. Oxidative status was evaluated through the production of reactive oxidative species (ROS), total antioxidant capacity and lipid peroxidation. High concentrations of BHBA decreased the curvilinear velocity, straight line velocity, mean path velocity, linearity, straightness and hyperactivity of spermatozoa. However, there was no effect of BHBA on oxidative and antioxidant capacity as well as on sperm morphology. In conclusion, exposure of bovine spermatozoa to high levels of BHBA impairs sperm kinetics without altering oxidative and antioxidant mechanisms.

A drastic shift in the energetic landscape of toothed whale sperm cells

Mammalian spermatozoa are a notable example of metabolic compartmentalization.¹ Energy in the form of ATP production, vital for motility, capacitation, and fertilization, is subcellularly separated in sperm cells. While glycolysis provides a local, rapid, and low-yielding input of ATP along the flagellum fibrous sheath, oxidative phosphorylation (OXPHOS), far more efficient over a longer time frame, is concentrated in the midpiece mitochondria.² The relative weight of glycolysis and OXPHOS pathways in sperm function is variable among species and sensitive to oxygen and substrate availability.^3-5 Besides partitioning energy production, sperm cell energetics display an additional singularity: the occurrence of sperm-specific gene duplicates and alternative spliced variants, with conserved function but structurally bound to the flagellar fibrous sheath.^6,7 The wider selective forces driving the compartmentalization and adaptability of this energy system in mammalian species remain largely unknown, much like the impact of ecosystem resource availability (e.g., carbohydrates, fatty acids, and proteins) and dietary adaptations in reproductive physiology traits.⁸ Here, we investigated the Cetacea, an iconic group of fully aquatic and carnivorous marine mammals, evolutionarily related to extant terrestrial herbivores.⁹ In this lineage, episodes of profound trait remodeling have been accompanied by clear genomic signatures.^10-14 We show that toothed whales exhibit impaired sperm glycolysis, due to gene and exon erosion, and demonstrate that dolphin spermatozoa motility depends on endogenous fatty acid β-oxidation, but not carbohydrates. Such unique energetic rewiring substantiates the observation of large mitochondria in toothed whale spermatozoa and emphasizes the radical physiological reorganization imposed by the transition to a carbohydrate-depleted marine environment.

Seasonally related metabolic changes and energy allocation associated with growth and reproductive phases in the liver of male goldfish (Carassius auratus)

Reproduction and growth follow a seasonal pattern in many fish species involving changes in gonadal development, growth, and metabolism. Significant metabolic energy is needed during gametogenesis in both female and male to produce hundreds of eggs and billions of sperms. Seasonal variations are controlled by the hormones of brain-pituitary-peripheral axis and are accompanied by significant metabolic changes. There is evidence that GnRH and GnIH are among the key neurohormones that regulate the reciprocal control of growth and reproduction. The objective of this study was to investigate changes in metabolic profile and energy allocation patterns at different stages of reproduction, using goldfish as a model organism and LC-MS as analytical platform for metabolic analysis. Goldfish undergoes a clear seasonal cycle of growth and reproduction. In vivo experiments were conducted at three different time point of the annual cycle: regressed gonadal phase (peak growth phase), mid gametogenesis and late gametogenesis. Emphasis is placed on changes in liver metabolic pathways to energetically sustain the physiological processes related to growth and reproduction. Moreover, we tested the hypothesis that GnRH and GnIH may play a role in the regulation of metabolism by investigating acute effects of these peptides at different stages of reproductive cycle. SIGNIFICANCE: The findings in this paper provide novel information on the seasonal changes in basal metabolism during different stages of reproductive cycle, and evidence for differential allocation of energy during reciprocal control of reproduction and growth in goldfish. Chemometrics combined with pathway-driven bioinformatics elucidated a shift in the metabolic profile, indicating distinct patterns of energy allocation in the reproductive and growth seasons. Furthermore, to our knowledge this is the first study to provide evidence for a possible regulatory role of GnRH and GnIH in liver metabolism and energy allocation patterns associated with growth and reproductive processes. Together our findings present a framework for better understanding of the hormonally induced changes in metabolism to energetically sustain growth and reproduction in fish and other oviparous species undergoing seasonal cycle.

1H NMR-based metabonomics for infertility diagnosis in men with varicocele

PURPOSE

"Omics" techniques have been used to understand and to identify biomarkers of male infertility. We report on the first metabonomics models created to diagnose varicocele and infertility among men with varicocele.

METHODS

We recruited 35 infertile men with varicocele (VI group), 21 fertile men with varicocele (VF group) and 24 fertile men without varicocele (C group). All men underwent standard semen analysis, scrotal duplex ultrasonography, and sexual hormone level measurement. Hydrogen-1 nuclear magnetic resonance (1H NMR) spectra of seminal plasma were used to create metabonomics models to discriminate between men with and without varicocele, and between fertile and infertile men with varicocele.

RESULTS

Using the statistical formalisms partial least square discriminants analysis and genetic algorithm-based linear discriminant analysis (GA-LDA), we created two models that discriminated the three groups from each other with accuracy of 92.17%. We also created metabonomics models using orthogonal partial least square discriminants analysis and GA-LDA that discriminated VF group from VI group, with an accuracy of 94.64% and 100% respectively. We identified 19 metabolites that were important in group segregation: caprate, 2-hydroxy-3-methylvalerate, leucine, valine, 3-hydroxybutyrate, lactate, alanine, 4-aminobutyrate, isoleucine, citrate, methanol, glucose, glycosides, glycerol-3-phosphocoline, n-acetyltyrosine, glutamine, tyrosine, arginine, and uridine.

CONCLUSIONS

1HNMR-based metabonomics of seminal plasma can be used to create metabonomics models to discriminate between men with varicocele from those without varicocele, and between fertile men with varicocele from those infertile with varicocele. Furthermore, the most important metabolites for group segregation are involved in the oxidative stress caused by varicocele.

Probing human sperm metabolism using 13C-magnetic resonance spectroscopy

STUDY QUESTION

Can 13C-Magnetic Resonance Spectroscopy (MRS) of selected metabolites provide useful information about human sperm metabolism and how glycolysis or oxidative phosphorylation are used by different sperm populations?

SUMMARY ANSWER

Sperm populations, prepared by density gradient centrifugation (DGC) and incubated with either 13Cu-glucose, 13Cu-fructose or 13C1-pyruvate, showed consistent evidence of metabolism generating principally lactate and more intermittently bicarbonate, and significantly more lactate was produced from 13Cu-glucose by vital or motile sperm recovered from the 40/80% interface compared to those from the pellet, which could not be accounted for by differences in the non-sperm cells present.

WHAT IS KNOWN ALREADY

Previous studies have focused on CO2 or other specific metabolite production by human sperm and there remains considerable debate about whether glycolysis and/or oxidative phosphorylation is the more important pathway for ATP production in sperm.

STUDY DESIGN, SIZE, DURATION

Sperm populations were prepared by DGC and subjected to 13C-MRS to answer the following questions. (i) Is it possible to detect human sperm metabolism of 13C substrates implicated in energy generation? (ii) What are the kinetics of such reactions? (iii) Do different sperm populations (e.g. '80%' pellet sperm and '40%' interface sperm) utilise substrates in the same way? Semen samples from 97 men were used in these experiments; 52 were used in parallel for aims (i) and (ii) and 45 were used for aim (iii).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm populations were prepared from ejaculates of healthy men using a Percoll/Phosphate Buffered Saline (PBS) DGC and then incubated with a range of 13C-labelled substrates (13Cu-glucose, 13Cu-fructose, 13C1-pyruvate, 13C1-butyrate, 13C3-lactate, 13C2,4-D-3-hydroxybutyrate, 13C5-l-glutamate, 13C1,2-glycine or 13Cu-galactose) along with penicillin/streptomycin antibiotic at 37°C for 4 h, 24 h or over 48 h for an estimated rate constant. Sperm concentration, vitality and motility were measured and, for a subset of experiments, non-sperm cell concentration was determined. A 9.4 T magnetic resonance spectrometer was used to acquire 1D 13C, inverse gated 1H decoupled, MRS spectra. Spectrum processing was carried out using spectrometer software and Matlab scripts to determine peak integrals for each spectrum.

MAIN RESULTS AND THE ROLE OF CHANCE

13Cu-glucose, 13Cu-fructose and 13C1-pyruvate were consistently converted into lactate and, to a lesser extent, bicarbonate. There was a significant correlation between sperm concentration and lactate peak size for 13Cu-glucose and 13Cu-fructose, which was not observed for 13C1-pyruvate. The lactate peak did not correlate with the non-sperm cell concentration up to 6.9 × 106/ml. The concentration of 13Cu-glucose, 13Cu-fructose or 13C1-pyruvate (1.8, 3.6, 7.2 or 14.4 mM) had no influence on the size of the observed lactate peak over a 4 h incubation. The rate of conversion of 13C1-pyruvate to lactate was approximately three times faster than for 13Cu-glucose or 13Cu-fructose which were not significantly different from each other. After incubating for 4 h, the utilisation of 13Cu-glucose, 13Cu-fructose or 13C1-pyruvate by sperm from the '40%' interface of the DGC was no different from those from the pellet when normalised to total sperm concentration. However, after normalising by either the vital or motile sperm concentration, there was a significant increase in conversion of 13Cu-glucose to lactate by '40%' interface sperm compared to pellet sperm (Vital = 3.3 ± 0.30 × 106 vs 2.0 ± 0.21 × 106; P = 0.0049; Motile = 7.0 ± 0.75 × 106 vs 4.8 ± 0.13 × 106; P = 0.0032. Mann-Whitney test P < 0.0055 taken as statistically significant). No significant differences were observed for 13Cu-fructose or 13C1-pyruvate.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

Only 13C labelled metabolites that accumulate to a sufficiently high concentration can be observed by 13C MRS. For this reason, intermediary molecules in the metabolic chain are difficult to observe without trapping the molecule at a particular step using inhibitors. Non-sperm cell concentration was typical of the general population and no link was found between these cells and the magnitude of the 13C-lactate peak. However, it is possible that higher concentrations than the maximum observed (6.9 × 106/ml) may contribute to exogenous substrate metabolism in other experiments.

WIDER IMPLICATIONS OF THE FINDINGS

13C-MRS can provide information on the underlying metabolism of multiple pathways in live sperm. Dysfunction in sperm metabolism, as a result of either impaired enzymes of lack of metabolisable substrate, could be detected in sperm by a non-destructive assay, potentially offering new treatment options to improve overall sperm quality and outcomes for reproduction.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by the Medical Research Council Grant MR/M010473/1. The authors declare no conflicts of interest.

mtDNA polymorphism and metabolic inhibition affect sperm performance in conplastic mice

Whereas a broad link exists between nucleotide substitutions in the mitochondrial genome (mtDNA) and a range of metabolic pathologies, exploration of the effect of specific mtDNA genotypes is on-going. Mitochondrial DNA mutations are of particular relevance for reproductive traits, since they are expected to have profound effects on male specific processes as a result of the strict maternal inheritance of mtDNA. Sperm motility is crucially dependent on ATP in most systems studied. However, the importance of mitochondrial function in the production of the ATP necessary for sperm function remains uncertain. In this study, we test the effect of mtDNA polymorphisms upon mouse sperm performance and bioenergetics by using five conplastic inbred strains that share the same nuclear background while differing in their mitochondrial genomes. We found that, while genetic polymorphisms across distinct mtDNA haplotypes are associated with modification in sperm progressive velocity, this effect is not related to ATP production. Furthermore, there is no association between the number of mtDNA polymorphisms and either (a) the magnitude of sperm performance decrease, or (b) performance response to specific inhibition of the main sperm metabolic pathways. The observed variability between strains may be explained in terms of additive effects of single nucleotide substitutions on mtDNA coding sequences, which have been stabilized through genetic drift in the different laboratory strains. Alternatively, the decreased sperm performance might have arisen from the disruption of the nuclear DNA/mtDNA interactions that have coevolved during the radiation of Mus musculus subspecies.

Germ cells regulate 3-hydroxybutyrate production in rat Sertoli cells

Paracrine regulation of Sertoli cell function by germ cells is an outstanding characteristic of testicular physiology. It has been demonstrated that Sertoli cells produce ketone bodies and that germ cells may use them as energy source. The aim of the study was to analyze a possible regulation by germ cells of ketogenesis in Sertoli cells. Cultures of Sertoli cells (SC) obtained from 31-day-old rats were co-cultured with germ cells (GC). The results presented herein show that the presence of GC stimulated 3-hydroxybutyrate production and increased mRNA levels of two enzymes involved in ketogenesis-carnitine palmitoyltransferase 1a (CPT1a) and mitochondrial 3-hydroxy-3-methylglutaryl-CoA (mHMGCoA) synthase- in SC. Additionally, GC increased monocarboxylate transporter 4 (Mct4) expression in SC, a transporter involved in ketone bodies exit. To evaluate if the observed effects might be mediated by soluble factors, SC cultures were incubated with germinal cell-conditioned medium (GCCM) or with two growth factors, bFGF and IGF1, which are known to be secreted by GC. We observed that GCCM and bFGF stimulated ketone bodies production but that IGF1 did not modify it. Also, we observed that GCCM and bFGF increased Cpt1a and Mct4 mRNA levels. In summary, results presented herein demonstrate that Sertoli cells are able to produce ketone bodies and that its production is regulated in a paracrine way by germ cells. This study adds new information about communication between Sertoli cells and developing germ cells.

Comparative Proteomic Identification of Mature and Immature Sperm in the Catfish Cranoglanis bouderius

To understand the molecular responses of mature and immature sperm in the catfish Cranoglanis bouderius, we used the iTRAQ proteomics approach to perform proteomic profiling of spermatogenesis in C. bouderius. As a result, 1,941 proteins were identified, including 361 differentially expressed proteins, 157 upregulated proteins and 204 downregulated proteins in mature sperm relative to immature sperm. All of the identified proteins were categorized into seven types of subcellular localizations and three molecular functions and were found to be involved in nine biological processes. All of the differential proteins were involved in 235 different pathways. Moreover, we found that the tricarboxylic acid (TCA) pathway played an important role in the energy metabolism of sperm and that the EABB pathway was involved in the mechanism of spermatogenesis. Our study is the first to use the iTRAQ-based proteomic approach to analyze the catfish sperm proteome, and the results we obtained using this approach are valuable for understanding the molecular mechanisms of fish spermatogenesis.

Differences in ATP Generation Via Glycolysis and Oxidative Phosphorylation and Relationships with Sperm Motility in Mouse Species

Mouse sperm produce enough ATP to sustain motility by anaerobic glycolysis and respiration. However, previous studies indicated that an active glycolytic pathway is required to achieve normal sperm function and identified glycolysis as the main source of ATP to fuel the motility of mouse sperm. All the available evidence has been gathered from the studies performed using the laboratory mouse. However, comparative studies of closely related mouse species have revealed a wide range of variation in sperm motility and ATP production and that the laboratory mouse has comparatively low values in these traits. In this study, we compared the relative reliance on the usage of glycolysis or oxidative phosphorylation as ATP sources for sperm motility between mouse species that exhibit significantly different sperm performance parameters. We found that the sperm of species with higher oxygen consumption/lactate excretion rate ratios were able to produce higher amounts of ATP, achieving higher swimming velocities. Additionally, we show that the species with higher respiration/glycolysis ratios have a higher degree of dependence upon active oxidative phosphorylation. Moreover, we characterize for the first time two mouse species in which sperm depend on functional oxidative phosphorylation to achieve normal performance. Finally, we discuss that sexual selection could promote adaptations in sperm energetic metabolism tending to increase the usage of a more efficient pathway for the generation of ATP (and faster sperm).

Protein degradation and phosphorylation after freeze thawing result in spermatozoon dysfunction

Cryopreservation is widely used in many assisted conception units. Semen cryopreservation is the only proven method that offers many couples the chance to have children. However, spermatozoa are exposed to physical and chemical stressors during freezing and thawing that result in adverse changes in membrane lipid composition, sperm motility, viability, and acrosome status. Wang et al. (Proteomics 2014, 14, 298-310) evaluate the protein content of freeze-thawed sperm samples relative to that of fresh sperm samples from the same normozoospermic donors. Four proteins are verified via Western blot and immunofluorescent staining, which are putatively involved in spermatozoon dysfunction. These marked differences demonstrated by Wang et al. suggest that dysfunctional spermatozoon after cryopreservation may be due to protein degradation and protein phosphorylation.

Glycolysis plays an important role in energy transfer from the base to the distal end of the flagellum in mouse sperm

Many studies have been conducted to elucidate the relationship between energy metabolic pathways (glycolysis and respiration) and flagellar motility in mammalian sperm, but the contribution of glycolysis to sperm motility has not yet been fully elucidated. In the present study, we performed detailed analysis of mouse sperm flagellar motility for further understanding of the contribution of glycolysis to mammalian sperm motility. Mouse sperm maintained vigorous motility in the presence of substrates either for glycolysis or for respiration. By contrast, inhibition of glycolysis by alpha-chlorohydrine caused a significant decrease in the bend angle of the flagellar bending wave, sliding velocity of outer doublet microtubules and ATP content even in the presence of respiratory substrates (pyruvate or β-hydroxybutyrate). The decrease of flagellar bend angle and sliding velocity are prominent in the distal part of the flagellum, indicating that glycolysis inhibition caused the decrease in ATP concentration threrein. These results suggest that glycolysis potentially acts as a spatial ATP buffering system, transferring energy (ATP) synthesized by respiration at the mitochondria located in the basal part of the flagellum to the distal part. In order to validate that glycolytic enzymes can transfer high energy phosphoryls, we calculated intraflagellar concentration profiles of adenine nucleotides along the flagellum by computer simulation analysis. The result demonstrated the involvement of glycolysis for maintaining the ATP concentration at the tip of the flagellum. It is likely that glycolysis plays a key role in energy homeostasis in mouse sperm not only through ATP production but also through energy transfer.

Glycolysis and mitochondrial respiration in mouse LDHC-null sperm

We demonstrated previously that a knockout (KO) of the lactate dehydrogenase type C (Ldhc) gene disrupted male fertility and caused a considerable reduction in sperm glucose consumption, ATP production, and motility. While that study used mice with a mixed genetic background, the present study used C57BL/6 (B6) and 129S6 (129) Ldhc KO mice. We found that B6 KO males were subfertile and 129 KO males were infertile. Sperm from 129 wild-type (WT) mice have a lower glycolytic rate than sperm from B6 WT mice, resulting in a greater reduction in ATP production in 129 KO sperm than in B6 KO sperm. The lower glycolytic rate in 129 sperm offered a novel opportunity to examine the role of mitochondrial respiration in sperm ATP production and motility. We observed that in media containing a mitochondrial substrate (pyruvate or lactate) as the sole energy source, ATP levels and progressive motility in 129 KO sperm were similar to those in 129 WT sperm. However, when glucose was added, lactate was unable to maintain ATP levels or progressive motility in 129 KO sperm. The rate of respiration (ZO2) was high when 129 KO or WT sperm were incubated with lactate alone, but addition of glucose caused a reduction in ZO2. These results indicate that in the absence of glucose, 129 sperm can produce ATP via oxidative phosphorylation, but in the presence of glucose, oxidative phosphorylation is suppressed and the sperm utilize aerobic glycolysis, a phenomenon known as the Crabtree effect.

A systematic analysis of a deep mouse epididymal sperm proteome

Spermatozoa are highly specialized cells that, when mature, are capable of navigating the female reproductive tract and fertilizing an oocyte. The sperm cell is thought to be largely quiescent in terms of transcriptional and translational activity. As a result, once it has left the male reproductive tract, the sperm cell is essentially operating with a static population of proteins. It therefore is theoretically possible to understand the protein networks contained in a sperm cell and to deduce its cellular function capabilities. To this end, we performed a proteomic analysis of mouse sperm isolated from the cauda epididymis and confidently identified 2850 proteins, which to our knowledge is the most comprehensive sperm proteome for any species reported to date. These proteins comprise many complete cellular pathways, including those for energy production via glycolysis, beta-oxidation and oxidative phosphorylation, protein folding and transport, and cell signaling systems. This proteome should prove a useful tool for assembly and testing of protein networks important for sperm function.

Human sperm tail proteome suggests new endogenous metabolic pathways

Proteomic studies are contributing greatly to our understanding of the sperm cell, and more detailed descriptions are expected to clarify additional cellular and molecular sperm attributes. The aim of this study was to characterize the subcellular proteome of the human sperm tail and, hopefully, identify less concentrated proteins (not found in whole cell proteome studies). Specifically, we were interested in characterizing the sperm metabolic proteome and gaining new insights into the sperm metabolism issue. Sperm were isolated from normozoospermic semen samples and depleted of any contaminating leukocytes. Tail fractions were obtained by means of sonication followed by sucrose-gradient ultracentrifugation, and their purity was confirmed via various techniques. Liquid chromatography and tandem mass spectrometry of isolated sperm tail peptides resulted in the identification of 1049 proteins, more than half of which had not been previously described in human sperm. The categorization of proteins according to their function revealed two main groups: proteins related to metabolism and energy production (26%), and proteins related to sperm tail structure and motility (11%). Interestingly, a great proportion of the metabolic proteome (24%) comprised enzymes involved in lipid metabolism, including enzymes for mitochondrial beta-oxidation. Unexpectedly, we also identified various peroxisomal proteins, some of which are known to be involved in the oxidation of very long chain fatty acids. Analysis of our data using Reactome suggests that both mitochondrial and peroxisomal pathways might indeed be active in sperm, and that the use of fatty acids as fuel might be more preponderant than previously thought. In addition, incubation of sperm with the fatty acid oxidation inhibitor etomoxir resulted in a significant decrease in sperm motility. Contradicting a common concept in the literature, we suggest that the male gamete might have the capacity to obtain energy from endogenous pools, and thus to adapt to putative exogenous fluctuations.

Metabolic substrates exhibit differential effects on functional parameters of mouse sperm capacitation

Although substantial evidence exists that sperm ATP production via glycolysis is required for mammalian sperm function and male fertility, conflicting reports involving multiple species have appeared regarding the ability of individual glycolytic or mitochondrial substrates to support the physiological changes that occur during capacitation. Several mouse models with defects in the signaling pathways required for capacitation exhibit reductions in sperm ATP levels, suggesting regulatory interactions between sperm metabolism and signal transduction cascades. To better understand these interactions, we conducted quantitative studies of mouse sperm throughout a 2-h in vitro capacitation period and compared the effects of single substrates assayed under identical conditions. Multiple glycolytic and nonglycolytic substrates maintained sperm ATP levels and comparable percentages of motility, but only glucose and mannose supported hyperactivation. These monosaccharides and fructose supported the full pattern of tyrosine phosphorylation, whereas nonglycolytic substrates supported at least partial tyrosine phosphorylation. Inhibition of glycolysis impaired motility in the presence of glucose, fructose, or pyruvate but not in the presence of hydroxybutyrate. Addition of an uncoupler of oxidative phosphorylation reduced motility with pyruvate or hydroxybutyrate as substrates but unexpectedly stimulated hyperactivation with fructose. Investigating differences between glucose and fructose in more detail, we demonstrated that hyperactivation results from the active metabolism of glucose. Differences between glucose and fructose appeared to be downstream of changes in intracellular pH, which rose to comparable levels during incubation with either substrate. Sperm redox pathways were differentially affected, with higher levels of associated metabolites and reactive oxygen species generated during incubations with fructose than during incubations with glucose.

Proteomics-based study on asthenozoospermia: differential expression of proteasome alpha complex

With a view to understand the molecular basis of sperm motility, we have tried to establish the human sperm proteome by two-dimensional PAGE MALDI MS/MS analysis. We report identification of 75 different proteins in the human spermatozoa. Comparative proteome analysis was carried out for asthenozoospermic and normozoospermic patients to understand the molecular basis of sperm motility. Analysis revealed eight proteins (including one unidentified) with altered intensity between the groups. Differential proteins distributed into three functional groups: 'energy and metabolism' (triose-phosphate isomerase, glycerol kinase 2, testis specific isoform and succinyl-CoA:3-ketoacid co-enzyme A transferase 1, mitochondrial precursor); 'movement and organization' (tubulin beta 2C and tektin 1) and 'protein turnover, folding and stress response' (proteasome alpha 3 subunit and heat shock-related 70 kDa protein 2). It was interesting to note that although the proteins falling in the functional group of 'energy and metabolism' are higher in the asthenozoospermic patients, the other two functional groups contain proteins, which are higher in the normozoospermic samples. Validation of results carried out for proteasome alpha 3 subunit by immunoblotting and confocal microscopy, confirmed significant changes in intensity of proteasome alpha 3 subunit in asthenozoospermic samples when compared with normozoospermic controls. Significant positive correlation too was found between proteasome alpha 3 subunit levels and rapid, linear progressive motility of the spermatozoa. In our understanding, this data would contribute appreciably to the presently limited information available about the proteins implicated in human sperm motility.

Sorbitol can fuel mouse sperm motility and protein tyrosine phosphorylation via sorbitol dehydrogenase

Energy sources that can be metabolized to yield ATP are essential for normal sperm functions such as motility. Two major monosaccharides, sorbitol and fructose, are present in semen. Furthermore, sorbitol dehydrogenase (SORD) can convert sorbitol to fructose, which can then be metabolized via the glycolytic pathway in sperm to make ATP. Here we characterize Sord mRNA and SORD expression during mouse spermatogenesis and examine the ability of sorbitol to support epididymal sperm motility and tyrosine phosphorylation. Sord mRNA levels increased during the course of spermatogenic differentiation. SORD protein, however, was first detected at the condensing spermatid stage. By indirect immunofluorescence, SORD was present along the length of the flagella of caudal epididymal sperm. Furthermore, immunoelectron microscopy showed that SORD was associated with mitochondria and the plasma membranes of sperm. Sperm incubated with sorbitol maintained motility, indicating that sorbitol was utilized as an energy source. Sorbitol, as well as glucose and fructose, were not essential to induce hyperactive motility. Protein tyrosine phosphorylation increased in a similar manner when sorbitol was substituted for glucose in the incubation medium used for sperm capacitation. These results indicate that sorbitol can serve as an alternative energy source for sperm motility and protein tyrosine phosphorylation.

Sperm mitochondrial integrity is not required for hyperactivated motility, zona binding, or acrosome reaction in the rhesus macaque

Whether the main energy source for sperm motility is from oxidative phosphorylation or glycolysis has been long-debated in the field of reproductive biology. Using the rhesus monkey as a model, we examined the role of glycolysis and oxidative phosphorylation in sperm function by using alpha-chlorohydrin (ACH), a glycolysis inhibitor, and pentachlorophenol (PCP), an oxidative phosphorylation uncoupler. Sperm treated with ACH showed no change in percentage of motile sperm, although sperm motion was impaired. The ACH-treated sperm did not display either hyperactivity- or hyperactivation-associated changes in protein tyrosine phosphorylation. When treated with PCP, sperm motion parameters were affected by the highest level of PCP (200 microM); however, PCP did not cause motility impairments even after chemical activation. Sperm treated with PCP were able to display hyperactivity and tyrosine phosphorylation after chemical activation. In contrast with motility measurements, treatment with either the glycolytic inhibitor or the oxidative phosphorylation inhibitor did not affect sperm-zona binding and zona-induced acrosome reaction. The results suggest glycolysis is essential to support sperm motility, hyperactivity, and protein tyrosine phosphorylation, while energy from oxidative phosphorylation is not necessary for hyperactivated sperm motility, tyrosine phosphorylation, sperm-zona binding, and acrosome reaction in the rhesus macaque.

Hamster sperm capacitation: role of pyruvate dehydrogenase A and dihydrolipoamide dehydrogenase

Recently, we demonstrated that pyruvate dehydrogenase A2 (PDHA2) is tyrosine phosphorylated in capacitated hamster spermatozoa. In this report, using bromopyruvate (BP), an inhibitor of PDHA, we demonstrated that hamster sperm hyperactivation was blocked regardless of whether PDHA was inhibited prior to or after the onset of hyperactivation, but the acrosome reaction was blocked only if PDHA was inhibited prior to the onset of the acrosome reaction. Further, inhibition of PDHA activity did not inhibit capacitation-associated protein tyrosine phosphorylation observed in hamster spermatozoa. It is demonstrated that the essentiality of PDHA for sperm capacitation is probably dependent on its ability to generate effectors of capacitation such as reactive oxygen species (ROS) and cAMP, which are significantly decreased in the presence of BP. MICA (5-methoxyindole-2-carboxylic acid, a specific inhibitor of dihydrolipoamide dehydrogenase [DLD]), another component of the pyruvate dehydrogenase complex (PDHc), also significantly inhibited ROS generation and cAMP levels thus implying that these enzymes of the PDHc are required for ROS and cAMP generation. Furthermore, dibutryl cyclic adenosine monophosphate could significantly reverse the inhibition of hyperactivation observed in the presence of BP and inhibition of acrosome reaction observed in the presence of BP or MICA. The calcium ionophore, A23187, could also significantly reverse the inhibitory effect of BP and MICA on sperm acrosome reaction. These results establish that PDHA is required for hamster sperm hyperactivation and acrosome reaction, and DLD is required for hamster acrosome reaction. This study also provides evidence that ROS, cAMP, and calcium are involved downstream to PDHA.

The role of the mitochondrion in sperm function: is there a place for oxidative phosphorylation or is this a purely glycolytic process?

We review here the current knowledge related to the metabolic pathways used by spermatozoa to meet their high demands for ATP. This is discussed with special emphasis on one of their key roles, motility. We believe that the controversy among glycolytic and oxidative phosphorylation supporters is artificial and, as it happens in many other cell types, the source of ATP is multiple and depends on external inputs.

Glycolysis and sperm motility: does a spoonful of sugar help the flagellum go round?

It is doubtful that diffusion can deliver sufficient ATP from the mitochondria to sustain activity at the distal end of the sperm flagellum. Glycolytic enzymes bound to the fibrous sheath could provide energy along the flagellum at the point it is required. An obligatory role for glycolysis is supported by the lack of progressive motility in sperm from mice where the gene for sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDHs) had been 'knocked out'. Here, I review some evidence against this idea. First, pure diffusion from the mitochondrion is likely to be adequate in species with smaller sperm, and it is possible that rapid ATP delivery required in larger sperm could be achieved by an adenylate kinase shuttle. Second, experience with alpha-chlorohydrin demonstrates that sperm can remain motile with normal ATP concentrations despite inhibition of GAPDHs; adverse effects only occur if glucose is added and high levels of glycolytic intermediates accumulate. These observations undermine the GAPDHs knockout mouse as evidence for an essential role of local glycolysis. Third, sperm from many species can remain motile for long periods in sugar-free media and excepting dog sperm, evidence that gluconeogenesis is a possible explanation, is weak. In most species, it is unlikely that local glycolysis is the only way that ATP can be supplied to the distal flagellum.